1. Field of the Invention
The present invention relates to a circuit which determines the temperature of a device. More particularly, a complementary metal oxide semiconductor (CMOS) circuit is provided which uses a current source to generate charge and discharge voltages applied to a capacitor. These voltages are dependent on the temperature coefficient of a resistor in the current source. The charge and discharge times are then used to determine a frequency which is dependent on the temperature of the resistor. Thus, the temperature is sensed based on the output frequency of the circuit.
2. Description of Related Art
In the computer and data processing industry there is an ever increasing demand for higher processing speeds and systems which are capable of performing multiple tasks in parallel. Often times there are tradeoffs associated with this increased processing performance. One example is an increased level of power consumption and corresponding increase in the amount of heat generated by a particular device or IC.
Temperature sensors have many applications. A large number of circuits and/or functional units in today""s electronic devices are temperature sensitive and require accurate and reliable temperature information in order to take corrective action when the temperature becomes too high. For example, the system frequency may be reduced when a certain temperature threshold is reached in order to cause the temperature to be reduced below the critical point. Further, systems, such as portable electronic devices (games, laptops, notebook computers, personal digital assistants), and the like are sensitive to power consumption and may need to shut down all or part of their operations when the power, which is function of temperature, reaches a certain level. Additionally, some individual circuits may need to be disconnected or shut down when the temperature reaches a predetermined level. Another application is an oscillator, such as a crystal oscillator which is frequency dependent. In this case a temperature sensor is required to adjust the accuracy of the output frequency. Rechargeable battery applications is yet another area wherein an accurate and reliable temperature sensor will have utility.
Conventional temperature sensing techniques are typically based on a predetermined value of a transistor threshold voltage. In reality the integrated circuit (IC) fabrication process is not exactly consistent between groups of wafers, or lots. Thus, a threshold voltage for transistors in a particular lot of wafers will not be the same as the threshold voltage for the transistors in another lot. Thus, the correlation between the frequency and the temperature will not be consistent between sensors fabricated in different lots. The functional units relying on the temperature to perform various data processing activities may operate at different temperatures resulting in inconsistent results across the same device fabricated in a different lot.
Therefore, it can be seen that a need exists for a temperature sensor that provides greater consistency when manufactured at different times and in different lots in order to provide a temperature dependent output signal having increased accuracy.
In contrast to the prior art, the present invention is a temperature sensor which is based on the actual temperature coefficients of a device in the circuit, rather than a predetermined threshold voltage that varies across different devices.
Broadly, the present invention relates to a circuit which determines the temperature of a device. More particularly, CMOS circuit is provided which uses a current source to generate charge and discharge voltages applied to a capacitor. These voltages are dependent on the temperature coefficient of a resistor in the current source. The charge and discharge times are then used to determine a frequency which is dependent on the temperature of the resistor. Thus, the temperature is sensed based on the output frequency of the circuit.
An additional feature of the present invention is a mechanism which allows the temperature sensor to be activated or deactivated as needed.
Therefore, in accordance with the previous summary, objects, features and advantages of the present invention will become apparent to one skilled in the art from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.